In direct injection gasoline internal combustion engines known from the related art, gasoline is injected directly into the combustion chamber of a cylinder of the internal combustion engine. The gasoline-air mixture compressed in the combustion chamber is then ignited by the ignition from an ignition spark in the combustion chamber. The volume of the ignited gasoline-air mixture expands explosively and sets in motion a piston that is able to move back and forth in the cylinder. The back and forth motion of the piston is transmitted to a crankshaft of the internal combustion engine.
Direct injection internal combustion engines are able to be operated in various operating modes. A so-called stratified operation is known as a first operating mode, which is used especially in response to smaller loads. A second operating mode known is a so-called homogeneous operation, which is used in response to greater loads on the internal combustion engine. The various operating modes differ especially in the start of injection and the injection period, as well as the point of ignition.
In stratified operation, the gasoline is injected into the combustion chamber during the compression phase of the internal combustion engine in such a way that, at the time of ignition, there is a fuel cloud in the immediate surroundings of a spark plug. This injection can proceed in different ways. Thus, it is possible that the injected fuel cloud is at the spark plug already during, or immediately after the injection, and is ignited by it. It is also possible that the injected fuel cloud is supplied to the spark plug by a charge movement, and is only then ignited. In the case of both combustion methods there is no uniform fuel distribution present in the combustion chamber, but rather a stratified charge.
An advantage of the stratified operation is that, using a very slight quantity of fuel, the smaller loads present are able to be carried out by the internal combustion engine. Greater loads, however, cannot be satisfied by stratified operation.
In the homogeneous operation used for greater loads, the gasoline is injected during the intake phase of the internal combustion engine, so that a swirl (voracity), and thereby a distribution, of the gasoline in the combustion chamber is able to take place even before ignition without a problem. To that extent, homogeneous operation corresponds approximately to the operating manner of internal combustion engines in which, in the usual way, fuel is injected into the intake pipe. If necessary, one may also use homogeneous operation for smaller loads.
In the operation of an internal combustion engine in the HCCI mode (homogeneous charge compression ignition), which is sometimes also designated as CAI (controlled auto ignition), ATAC (active thermo atmosphere combustion) or TS (Toyota Soken), the ignition of the air-fuel mixture does not take place by spark ignition, but by controlled self-ignition. The HCCI combustion process may be brought about, for instance, by a high proportion of hot residual gases and/or by a high compression and/or a high intake air temperature. A prerequisite for the self-ignition is a sufficiently high energy level in the cylinder. Internal combustion engines that are able to be operated in the HCCI mode are described in U.S. Pat. No. 6,260,520, U.S. Pat. No. 6,390,054, German Patent No. DE 199 27 479 and PCT International Patent Publication No. WO 98/10179.
By contrast to a usual combustion having spark ignition, the HCCI combustion has the advantage of reduced fuel usage and lower pollutant emission. To be sure, the regulation of the combustion process and especially the control of the self-ignition of the mixture is complex. Thus, what is needed is a regulation of the actuating variables that influence the combustion process for, for instance, the fuel injection (injection quantity and start and duration of injection) internal or external exhaust gas recirculation, intake valves and exhaust valves (variable valve control), exhaust gas back pressure (exhaust gas flap), possibly ignition support, intake air temperature, fuel quality and compression ratio in the case of internal combustion engines having variable compression ratios.
At this time, controlled self-ignition is only able to be used within narrow load ranges, since self-ignition is only driven by its kinetics of reaction, at present.
Therefore, the present invention is based on the object of widening the load ranges that are usable for Otto engine self-ignition.